Volvo C70 subs

Hi I have a 2001 Volvo C70 convertible and have some question about how to install new subs, I will give you some information about the system so you know what I am working with.

The C70 has a very nice factory sound system it has 11 speakers, 2 tweeters & a 7in center channel in that dash that has its own small amp. Each door has a 8ohm 4in mid & high and a 8in 8ohm sub-woofer in each door. The speakers are wired in parallel so the 400 watt Alpine V12 sees 4ohms on each of its 4 channels. In the back their is a 8ohm 6.5 on each side and 2 8ohm 8in sub-woofers that are built into / behind the back seat. Each sub-woofer is wired parallel to a 6.5. Each set of sub & mid/high has their own crossover.

My plan is to replace the 4in in the doors with 6.5 4ohm speakers and replace the rear 6.5 with a 4ohm speakers and run them off the factory install Alpine V12. I was planning on install MB Quarts FSB216 6.5speakers.

Their is a wiring kit that I can get that allows me to run two set of RCA's from the cable that connects to the factor amp. I plan to use those RCA's for my subs.

My problems & question is with my sub installation, I am planning to run MB Quarts 8" RLP204 subs because they have a reduced mounting depth that will work for my front doors and rear installation. I plan to power the subs with a MB Quarts FX4.100 witch would send each sub 200watts RMS at 2ohms, the subs are 4ohm dual voice coil.

My problem is that the subs are designed to be installed in rather small enclosures and by mounting them in the door they would have to be free-air, I've been looking at the doors and I can sound dampen them and try to seal the sub so that the front & back waves stay separate "I've heard that is important for free-air subs" I am wondering how the subs will sound free-air? Their frequency response is 35-120HZ & 81.23DB can I use the gain on the amp to tone-down the subs so I don't have to-much bass up front or is it impossible to have to much bass up front?

My rear subs are positioned behind the back seat cushion and fire forward. I haven't taken the rear seat out to inspect how I can possibly seal their enclosures but it should be possible because I did find some pics online of what I am working with.

Do you think that my bass will sound ok having two different enclosures and with my rear subs firing into the seat? The car is a convertible so bass is hard to get but do you think the system will sound good with 800watts RMS going to 4 8's?
Thanks for any input

Re: Volvo C70 subs

So by treating the doors do you mean sound dampening them and up-grading by installing new 6.5 and a 8 in each door?

I understand that enclosure design is very important but can free-air subs still sound good? If I sound dampen the doors and try to seal them?

I talked a to a local stereo shop and he said just do your best and see how it sounds, because if your subs are only getting about 20watts RMS each now and you up-grade your subs and throw 720 more watts RMS at them then you will make an improvement.